21 8 BRAINS OF RATS AND MEN 



whose "set" gives us the new behavior pattern may 

 not be represented in the cortex. This would be true, 

 probably, of only the simpler trial-and-error habits. 

 In more complex behavior the initial learning pattern 

 is cortical as well as thalamic and in higher animals 

 perhaps exclusively cortical in some cases. 



The cortex of the rat contains projection centers 

 (apparently ill defined at their borders), each with 

 characteristic subcortical connections and each with 

 specific functional significance. To this extent cortical 

 localization of function is definitely established. This 

 cortex is not physiologically equipotential. There is, 

 moreover, evidence that some cortical influence of a 

 very generalized character (probably reinforcement, 

 tonic activation, or facilitation of some sort) can be 

 exerted upon subcortical activities in non-localizable 

 ways. 



In the more complex forms of individually ac- 

 quired behavior the intrinsic functions of the cortex 

 apparently involve co-operative action of several 

 physiologically diverse cortical fields mediated by the 

 association fibers. In the rat this associational tissue 

 is for the most part knit in with the projection centers 

 as defined above. There is no evidence of extensive 

 areas of purely associational cortex such as are so 

 characteristic of higher brains, nor does the rat exhibit 

 any behavior requiring the use of such associational 

 mechanism. 



It seems probable that the rat's cortex exerts a 



